1. Field of the Invention
The present invention relates to a wireless communication apparatus and a method of preventing leakage of an encrypted key.
Priority is claimed on Japanese Patent Application No. 2011-156622, filed Jul. 15, 2011, the content of which is incorporated herein by reference.
2. Description of the Related Art
Wireless communication systems have advantages in that it is not necessary to wire connection lines connecting wired communication apparatuses to each other and it is easy to install wireless communication apparatuses in places in which wiring is difficult or places in which wiring is not economical. Therefore, in recent years, wireless communication systems have frequently been utilized in various fields. For example, in plants or factories, wireless communication system are realized in such a manner that work field apparatuses such as measurement apparatuses or operation apparatuses, called wireless field apparatuses, capable of performing wireless communication are installed, and control signals used to control the wireless field apparatuses or measurement signals or the like obtained from the wireless field apparatuses are communicated via wireless communication networks.
In such a wireless communication system, various kinds of information communicated via wireless communication networks are encrypted using encryption technology such as shared key encryption schemes in many cases, since it is necessary to ensure security. In the shared key encryption schemes, it is necessary to set a shared key in the wireless communication apparatuses in advance before the wireless communication apparatuses start wireless communication, since a scheme of using the same key, which is called a shared key, is used in encrypting and decrypting processes.
For example, in many cases, manufacturers set a shared key in the wireless communication apparatuses when manufacturing the wireless communication apparatuses or users manually set a shared key in wireless communication apparatuses when starting to use the wireless communication apparatuses. A method of setting a shared key in accordance with a public key encryption scheme is also used as well as the setting method. According to the public key encryption scheme, the shared key is set by transmitting the shared key encrypted using the public key to a wireless communication apparatus and allowing the wireless communication apparatus to decrypt the shared key using a preset private key.
The method of setting a shared key by using the above-described public key encryption scheme is used in over the air (OTA) public key infrastructure (PKI) provisioning that is defined in conformity with a wireless communication standard such as ISA100.11a. ISA100.11a is an industrial automation wireless communication standard that is designed by the International Society of Automation (ISA). Further, a shared key is set according to the above-described public key encryption scheme in “An Interoperable Authentication System using ZigBee-enabled Tiny Portable Device and PKI” by Ki Woong Park et al., in Computer Engineering Research Lab., Department of Electrical Engineering and Computer Science, Korea Advanced Institute of Science and Technology.
In the wireless communication apparatus in which a shared key is set according to the above-described public key encryption scheme, a function, which is hereinafter referred to as a “public key encryption processing function”, of decrypting an encrypted shared key using a public key and a function, which is hereinafter referred to as a “shared key encryption processing function”, of encrypting and decrypting information to be communicated using the shared key may be mounted on a single chip. If the private key and the shared key are implemented in a single chip and access to such information is requested, the information may be prevented from being leaked to a third party in a tamper-proof configuration designed to destroy all of the information and the security may be improved.
In some cases, the public key encryption processing function and the shared key encryption processing function may not be mounted on a single chip. In these cases, for example, a module, which is hereinafter referred to as a “public key encryption processing module”, on which the public key encryption processing function is mounted and a module, which is hereinafter referred to as a “wireless communication module”, on which the shared key encryption processing function is mounted and which performs wireless communication are separately provided, a transceiver such as a universal asynchronous receiver transmitter (UART) is provided in each module, and a connection bus connects the modules to each other.
In this configuration, operations (1) to (3) can be performed:
(1) substituting the public key encryption processing module and the wireless communication module;
(2) changing operation modes of the public key encryption processing module and the wireless communication module; and
(3) referring to communication contents transmitted via the connection bus or the like.
As described in operation (1), for example, when the wireless communication module is substituted, the shared key decrypted by the public key encryption processing module may be handed to the substituted wireless communication module. Therefore, the shared key can be referred to. Further, as described in operation (2), for example, when an operation mode of each module is changed to a “debug mode,” any one of the shared key used in the wireless communication module and the private key used in the public key encryption processing module can be referred to.
Furthermore, as described in operation (3), when the communication contents are referred to via the connection bus or the like, the shared key or the private key transmitted and received between the public key encryption processing module and the wireless communication module can be referred to. Thus, when a third party who bears ill will performs one of operations (1) to (3), there is a concern that the shared key or the private key which should be kept secret may be leaked.